Dana Vollmer knew 2016 would be a significant year: Her son, Arlen, would turn 1. He’d start to walk and talk.

But it wasn’t going to be a landmark swimming year for her. She was already retired. One year after winning three gold medals at the London Olympics, Vollmer, who swam collegiately at Cal, left the sport.

She wasn’t. And now Vollmer, who won the 100-meter butterfly at the winter national championships this month, looks like a strong bet to make her third Olympic team and compete in Rio de Janeiro in August. And if that comes to pass, she’ll certainly be one of the athletes for Bay Area sports fans to watch in 2016.

Her retirement wasn’t a shock. Vollmer, now 28, had overcome an injury-filled, stressful career to reach glory in 2012. What better time to step away? But for some reason, she declined to officially sign her retirement papers. Her coach, Teri McKeever, let her know that there was still plenty of room for her in the butterfly.

Her return was surprising, particularly because the decision was made at the unlikely moment of her eighth month of pregnancy, while she was on bed rest because of early contractions.

“I wanted my body back,” she said. “I wanted to make swimming part of a lifestyle I love.”

Vollmer burst on the scene in 2000, when at age 12 she was the youngest swimmer to compete at the Olympic trials. Four year later, at age 16, she won a gold medal on the world-record-setting 4x200-freestyle relay team.

But in the following Olympic cycle, expectations grew, Vollmer struggled with injury and she froze at the 2008 Olympic trials, just missing making the team in any of her events.

“I just crumbled under the pressure,” she said. “I was more afraid of disappointing people than feeling excited. It was a paralyzing place to be.”

McKeever thinks that if Vollmer didn’t have one more year of eligibility at Cal, she would have walked away from the sport. It was that devastating.

“But I think if she had made the (2008) team, I don’t think she breaks the world record or wins gold or is as good as she was in 2012,” McKeever said.

Between 2008 and 2012, Vollmer did a lot of mental work. She talked with a sports psychologist who helped her take off the pressure in training. She also worked with a therapist away from sports, who helped her understand why she was putting so much pressure on herself.

During that Olympic cycle, Vollmer married Andy Grant, who swam at Stanford. That gave her life a new balance heading into the London Olympics.

“By 2012, I felt much more confident in myself,” she said. “I felt my life wasn't going to crumble if I didn’t make the Olympic team. I had more freedom to get up there and try.”

Photo: Paul Chinn / Paul Chinn / The Chronicle

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Olympic gold medalist and former Cal swimmer Dana Vollmer trains with the Bears swim team at UC Berkeley earlier in December.

Olympic gold medalist and former Cal swimmer Dana Vollmer trains with the Bears swim team at UC Berkeley earlier in December.

Photo: Paul Chinn / Paul Chinn / The Chronicle

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Olympic gold medalist and former Cal swimmer Dana Vollmer (silver cap) trains with the Bears swim team at UC Berkeley.

Olympic gold medalist and former Cal swimmer Dana Vollmer (silver cap) trains with the Bears swim team at UC Berkeley.

Photo: Paul Chinn / Paul Chinn / The Chronicle

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Olympic gold medalist and former Cal swimmer Dana Vollmer trains with the current Bears swim team at UC Berkeley on Friday, Dec. 18, 2015.

Olympic gold medalist and former Cal swimmer Dana Vollmer trains with the current Bears swim team at UC Berkeley on Friday, Dec. 18, 2015.

Photo: Paul Chinn / The Chronicle

Olympian Dana Vollmer back in pool and aiming for Rio

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The confidence showed in the pool. In London, she set a world record in her signature event, the 100 butterfly, with a time of 55.98 seconds. She won two other gold medals, in the 800-meter free relay and the 400-meter medley relay, helping her team set a world record in the latter event.

Baby Arlen adds another layer of balance to her life. After making the decision to come back in February, Vollmer gave birth in March and was back in the pool at Cal by May. She returned to working with McKeever, who has been with her through the ups and downs of her career.

McKeever, the first woman to serve as the head coach of the women’s swim team, led the American women to a dominating performance in London: a total of 12 medals, including six golds. Despite that, she was replaced by David Marsh, who served as one of her assistants in 2012. McKeever might travel to Rio as an assistant coach.

Vollmer, who lives in Danville, has been pleased with how quickly her body bounced back into shape. Last summer, she swam at the summer nationals while breastfeeding several times a day and placed fourth at the national championships in the 100 butterfly.

“I loved breastfeeding, but it drained the life out of me,” she said.

Now, Vollmer says she feels stronger and healthier than she ever has in her career.

“I feel happier with my sport than I ever have been,” she said. “I’m super excited to get up and train. I just have a better balance. It’s a different journey.”

The journey will take her to Australia in March for a month of training. She has the full support of her family and husband, who works as a computer-security consultant.

“He’s used to the 4:30 a.m. alarm clock,” Vollmer said. “It’s nice having someone I can kick around different ideas. Someone who not only supports me but loves watching swimming.”

The journey will also take her to Omaha, Neb., for the Olympic trials in early July. And, she hopes, to Rio for her third Olympics.

“She’s a different person now,” McKeever said. “She’s taken another step. She has perspective and is competing full of possibility and joy, not fear. There's a calmness and groundedness about her now.”

To commemorate the conclusion of 2015, while looking forward to 2016, the Sporting Green is profiling the top personalities Bay Area sports fans should focus on in the new year. For our full coverage of “People to Watch in 2016,” go to www.sfchronicle.com.